I did something similar to bypass Verizons $5 per month surcharge to tether. I think it was a different variable I set though, not tether_dun_required. I think it was something like don't check if the tether enable bit is 1. I haven't tethered in several years and several Verizon plan types though.
Iirc they did until they got in a bidding war with Google for the RF spectrum. Google bid Pi billion dollars, which pushed the government contract into a net neutrality clause that forced tethering to be free.
